ELTEC Uses FAA Standard for RRFB Dimming
On September 27, 2012, the FHWA determined that daytime dimming of RRFB (Rectangular Rapid Flashing Beacon) indications is not allowed. “The effectiveness of RRFBs depends upon the light output from the RRFB signal indications meeting the SAE J595 requirements for peak luminous intensity (candelas) for Class 1 at all time during daylight hours.” Dimming at night is acceptable since the “RRFB signal indications are so bright that they cause excessive glare during nighttime conditions.”
Traditional photocells designed to control outdoor lighting typically activate at dusk to allow luminaires to come up to full brightness before night. To provide nighttime dimming and meet the intent of the FHWA, the threshold for dimming activation required a more tailored approach that was realized using ELTEC’s custom built photo cell and establishing an ambient light level that appropriately defined the threshold for ‘night time’ conditions.
ELTEC determined that an acceptable standard for ambient light conditions which defines ‘night time’ are set forth by the FAA (Federal Aviation Administration) 14 CFR 61.57. This standard defines night as the period beginning one hour after sunset and ending one hour before sunrise. Based upon this definition, ELTEC programs their RRFB flasher to initiate the night dimming feature when ambient light conditions reach a level which is typical of the average ambient light level measured by the photocell one hour after sunset as determined empirically through testing.